This invention relates generally to sensor systems and more particularly to a thermal sensor system which detects incipient wheel journal bearing overheating on rail vehicles and activates the air brakes to stop the vehicle prior to bearing failure and possible derailment.
Railroad journal bearing failures due to overheating resulting in axle-end fracture and consequent dropping of the rail car sideframe to the roadway have been a most prevalent source of major accidents. These failures, called "hotboxes", if not detected in time, may lead to accidents that result in losses of millions of dollars and risk the lives of persons aboard the train, or in the vicinity, particlarly where hazardous cargoes are involved.
Present methods of detecting hotboxes include inspection in train yards and from passing trains by railroad personnel. Along main lines, bearing temperatures are monitored in route by automatic, track-side, infrared detectors. Inspection by railroad personnel is, however, time-consuming and costly since each journal box has to be individually checked. Automatic wayside infrared detection stations have been installed at several hundred locations. These units, capable of scanning each bearing on a passing train and reporting and/or recording its temperature, have been developed to a point of excellent effectiveness. However, at a cost of approximately $50,000 each, plus data transmission equipment to automatic signals or manned monitoring points, they have not generally been installed on low-traffic-density lines or at close enough intervals on mainlines to detect all hotboxes before catastrophic failure can develop.
Higher speeds, heavier loads, extended runs and other factors have necessitated the increased use of more expensive roller bearings and improved bearing lubrication systems to reduce bearing failures. The reduction in bearing failures, however, has not brought about a corresponding decrease in hotbox-caused derailments because the rate of derailments per detected hotbox has increased, resulting in a relatively constant hotbox derailment total. The decreased rate of detection may be attributed to several factors, such as the more rapid progression from initiation of bearing failure to catastrophic assembly failure characteristic of roller bearings and the less detectable early signs of roller bearing failure than bearings with lubricator pads.
Actual axle failure from a hotbox occurs from heating to a temperature where the steel is significantly weakened, since nominal stress levels are low. The energy input available from the maximum torque input from one pair of wheels to a seized bearing assembly is sufficient to raise the axle-end steel to 1000.degree. F. in less than one minute. It is not likely that this concentrated an input will occur in an actual assembly, but it is apparent that failure can occur in a matter of a very few miles or minutes of travel. Continuous, automatic monitoring of each bearing may be expected to provide virtually 100% protection from this mode of failure, provided the thermal path to the sensor is as short as that from the bearing to the axle and there is no significant time lag in the sensor.
Once a trouble signal is generated at one of the sensor locations, e.g., at the journal housing, and amplified to a usable power level, economic logic dictates that it be transmitted to a single, on-car location to actuate the inter-car communication link input. Several aspects of any such system are vital. Parallel inputs into the communication link must be mutually compatible. Failure of one or more sensors should not impair system operation. System refurbishment after an actuation, if required at all, must be reasonably inexpensive and capable of accomplishment at relatively widespread and unsophisticated facilitites. Low cost over the complete life cycle, including all initial hardware costs, installation and check out, maintenance and repair, periodic continuity checks, and accommodation to other car maintenance procedures is vital to system. Demonstrable ruggedness and predictable life are particularly important to acceptance of a sensor system.